CVD金刚石涂层前预处理对硬质合金基体强度的影响

Influence of Pretreatment before CVD Diamond Coating Process on the Strength of Cemented Carbide Substrate

CVD金刚石涂层硬质合金刀具是有色金属及合金、石墨、陶瓷和碳纤维增强塑料(CFRP)等复合材料机械加工的理想刀具。但金刚石涂层前对WC-Co硬质合金基体的预处理过程在消除表面Co改善涂层附着力的同时也降低了基体强度。通过正交试验并采用SEM和EDS分析试样表面形貌和Co含量,采用XRD分析试样表层的相组成,研究了预处理对两种WC晶粒度的WC-6Co硬质合金基体强度的影响机制。结果表明:酸、碱预处理均显著降低基体强度,热处理则可消除酸碱处理对强度的不利影响。预处理对不同WC晶粒度的硬质合金基体强度的影响明显不同。粗晶硬质合金预处理后抗弯强度降低幅度更大,其抗弯强度的Weibull模数减小也更显著。相对而言,粗晶硬质合金的抗弯强度对酸腐蚀时间tC更敏感,而细晶硬质合金则受碱腐蚀时间tM的影响更大。因此,金刚石涂层前,应根据不同硬质合金基体的成分和微观结构匹配合适的预处理制度。

CVD diamond-coated cemented carbide tool is ideal for the machining of composite materials,including non-ferrous metals,alloys,graphite,ceramic,and carbon fiber reinforced plastic(CFRP).However,the pretreatment process of WC-Co cemented carbide substrate before diamond coating reduces the strength of the substrate while eliminating Co on the surface to improve the adhesion of the coating.The influence mechanism of pretreatment on the substrate strength of WC-6Co cemented carbides with two WC grain sizes was studied through orthogonal experiments.The surface morphology and Co content of the sample were analyzed by SEM and EDS,and the phase composition of the sample surface was analyzed by XRD.The results show that both acid and alkali pretreatment significantly decrease the strength of the substrate,while heat treatment can eliminate the unfavorable influence of acid and alkali treatment on the strength.The influence of pretreatment on the strength of cemented carbide substrate with different WC grain sizes is obviously different.In general,the decrease in transverse rupture strength(TRS)after pretreatment is greater for coarse-grained cemented carbides,and the Weibull modulus of TRS also decreases more significantly.Comparatively speaking,the TRS of coarse-grained cemented carbide is more sensitive to acid corrosion time,t_C,while that of fine-grained cemented carbide is more affected by alkali corrosion time,t_M.Therefore,an appropriate pretreatment system should be matched to the composition and microstructure of different cemented carbide substrates before diamond coating.